Senate Majority Leader Mitch McConnell urged President Trump to “exercise American leadership” and keep U.S. troops in northern Syria, saying that the president’s plan to remove forces from the area would only benefit U.S. enemies.

“American interests are best served by American leadership, not by retreat or withdrawal,” the Kentucky Republican said. He didn’t directly criticize the president, but reminded him that the Senate voted in January to keep U.S. troops in Syria, in reaction to a previous withdrawal plan announced by the White House.

The remarks by Mr. McConnell came amid a bipartisan outcry in Congress, and as lawmakers floated ways to punish Turkey if it moved ahead with a military incursion in the region.

On Monday morning, American military personnel began pulling back from the Syria-Turkey border, after Mr. Trump ordered the Pentagon to clear the way for Turkey to launch an offensive against U.S.-backed Kurdish fighters who have led the fight against Islamic State militants. Ankara considers the Kurdish fighters terrorists…